The main types of thermoset elastomers include polyurethanes, two-part silicones, and vulcanized rubber; each of theses elastomer has positive and negative attributes. Polyurethanes are formed from the reaction of a polyol and isocyanate and are preferred for the ease of processing, wide range of mechanical properties that can be obtained depending on the components chosen, and good adhesive properties to a range of substrates. Polyurethanes are generally limited in their thermal and hydrolytic stability.
Two-part cast silicone elastomers and vulcanized rubbers typically have thermal and hydrolytic stabilities that exceed polyurethanes, however; their application is generally limited to softer systems, less than about 80 Shore A, that normally require long cure and demold times, e.g., 15 hours or more. Vulcanized rubbers also require high temperature molding processes that limit their use in field applications, form fitting, or assembly applications without the use of additional primers and adhesives for bonding. Silicones can be cast at ambient temperatures but suffer the same deficiencies as vulcanized rubbers in terms of adhesion and are generally more expensive than urethane systems.
There therefore remains a need to have elastomer which has polyurethane like processing and mechanical properties with improved thermal and hydrolytic stabilities.